New Study Brings Antarctic Ice Loss Into Sharper Focus

A NASA study based on an innovative technique
for crunching torrents of satellite data provides the clearest picture yet of
changes in Antarctic ice flow into the ocean. The findings confirm accelerating
ice losses from the West Antarctic Ice Sheet and reveal surprisingly steady
rates of flow from its much larger neighbor to the east.

The computer-vision technique crunched data
from hundreds of thousands of NASA-U.S. Geological Survey Landsat satellite
images to produce a high-precision picture of changes in ice-sheet motion.

The new work provides a baseline for future
measurement of Antarctic ice changes and can be used to validate numerical ice
sheet models that are necessary to make projections of sea level. It also opens
the door to faster processing of massive amounts of data.

"We're entering a new age," said
the study's lead author, cryospheric researcher Alex Gardner of NASA's Jet
Propulsion Laboratory in Pasadena, California. "When I began working on this
project three years ago, there was a single map of ice sheet flow that was made
using data collected over 10 years, and it was revolutionary when it was
published back in 2011. Now we can map ice flow over nearly the entire
continent, every year. With these new data, we can begin to unravel the
mechanisms by which the ice flow is speeding up or slowing down in response to
changing environmental conditions."

The innovative approach by Gardner and his
international team of scientists largely confirms earlier findings, though with
a few unexpected twists.

Among the most significant: a previously
unmeasured acceleration of glacier flow into Antarctica's Getz Ice Shelf, on
the southwestern part of the continent -- likely a result of ice-shelf
thinning.

Speeding up in the west, steady flow in the
east

The research, published in the journal "The
Cryosphere," also identified the fastest speed-up of Antarctic glaciers during
the seven-year study period. The glaciers feeding Marguerite Bay, on the
western Antarctic Peninsula, increased their rate of flow by 1,300 to 2,600
feet (400 to 800 meters) per year, probably in response to ocean warming.

Perhaps the research team's biggest discovery,
however, was the steady flow of the East Antarctic Ice Sheet. During the study
period, from 2008 to 2015, the sheet had essentially no change in its rate of
ice discharge -- ice flow into the ocean. While previous research inferred a
high level of stability for the ice sheet based on measurements of volume and
gravitational change, the lack of any significant change in ice discharge had
never been measured directly.

The study also confirmed that the flow of West
Antarctica's Thwaites and Pine Island glaciers into the ocean continues to
accelerate, though the rate of acceleration is slowing.

In all, the study found an overall ice
discharge for the Antarctic continent of 1,929 gigatons per year in 2015, with
an uncertainty of plus or minus 40 gigatons. That represents an increase of 36
gigatons per year, plus or minus 15, since 2008. A gigaton is one billion tons.

The study found that ice flow from West
Antarctica -- the Amundsen Sea sector, the Getz Ice Shelf and Marguerite Bay on
the western Antarctic Peninsula -- accounted for 89 percent of the increase.

Computer vision

The science team developed software that
processed hundreds of thousands of pairs of images of Antarctic glacier
movement from Landsats 7 and 8, captured from 2013 to 2015.

These were compared to earlier radar satellite
measurements of ice flow to reveal changes since 2008.

"We're applying computer
vision techniques that allow us to rapidly search for matching features between
two images, revealing complex patterns of surface motion," Gardner said.

Instead of researchers comparing small sets of
very high-quality images from a limited region to look for subtle changes, the
novelty of the new software is that it can track features across hundreds of
thousands of images per year -- even those of varying quality or obscured by
clouds -- over an entire continent.

"We can now automatically generate maps of ice
flow annually -- a whole year -- to see what the whole continent is doing," Gardner
said.

The new Antarctic baseline should help ice
sheet modelers better estimate the continent's contribution to future sea level
rise.

"We'll be able to use this
information to target field campaigns, and understand the processes causing
these changes," Gardner said. "Over the next decade, all this is going to lead
to rapid improvement in our knowledge of how ice sheets respond to changes in
ocean and atmospheric conditions, knowledge that will ultimately help to inform
projections of sea level change."